Devices of this type are used in surgical procedures referred to in the art as cardiopulmonary bypass operations. During such procedure the normal function of the patient's heart and lungs is suspended, and the function of these organs is replaced by artificial blood handling and treating units in a life-sustaining extracorporeal blood flow circuit. In these procedures the main body of the patient's blood is typically withdrawn from the patient through a cannula inserted into the right atrium and passed through a filtered reservoir, a blood pump, a blood oxygenator, and an arterial blood filter before being returned to the patient through a cannula inserted into the aorta. The main blood stream is in accordance with typical practice combined with blood collected from the surgical field, which blood is gathered in one or more cardiac vacuum suckers and after defoaming and depth filtering collected in the reservoir, which is common for the two blood paths before being extracted through the blood outlet through an extracorporeal blood pump. A device Of this type is disclosed in EP-B-0 190 020.
For surgical Operations of this kind it is important to reduce the priming volume of the device, which is normally done by adapting the size of the device to the size of the patient. The known device comprises a number of elements arranged inside the filter for supporting the filter and the defoaming material and for providing the flow paths for the two blood streams within the filter. This is especially disadvantageous if the filter is to be made in a number of different sizes because of the large number of parts.
It is an object of the invention to provide a device in which the filter element does not contain internal support or flow control elements and in which an increased filter area is obtainable for a predetermined priming volume.
The device according to the invention is characteristic in that the housing above the bottom comprises a wall forming a ledge in said reservoir and defining a bottom wall in a portion of the reservoir with enlarged cross-section;
The arrangement of the filters side by side results in a compact construction of the device and a short path of the filtered blood from the filter to the reservoir. The filters may have a shape which increases the filter area compared with filters of circular cross-section.
Preferred embodiments of the invention are defined in the subclaims. The filters preferably have an oval cross-section and a rounded profile. This shape is suited for making the filters self-supporting and is providing a comparatively large filter area in relation to the volume inside the filter. The filters are preferably bonded into oval recesses in the cover and ledge of the housing forming a rigid fastening of thee filters. In order to ensure a smooth flow of blood into the reservoir, the ledge has a gradient towards an inclined part of the reservoir. This arrangement prevents the forming of bubbles in the filtered blood. The filters are made from blanks which are welded along the edges before being turned inside out. The welding seam contributes to the self-supporting capacity of the filters.
The invention will be described in detail with reference to a preferred embodiment thereof which is a disposable blood treatment and collection device shown in the drawing and for use in an extracorporeal blood flow circuit.